1. Field of the Invention
This invention pertains to pumping liquids from a well in the earth. More particularly, method and apparatus are provided for controlled gas lift system to pump liquid from a well.
2. Description of Related Art
Gas lift systems are used in the initial production of many oil and gas wells and are excellent systems to employ when the gas supply and reservoir pressure are adequate to produce the liquid in a gas conserving manner. After reduction of the reservoir gas pressure and thus the reservoir supply, one usually has to make a decision concerning the method of pumping when the reservoir pressure is not sufficient for economical regular gas lift to continue. Intermittent gas lift systems are often employed rather than beam pumps because of their flexibility, low initial capital cost per well pump, low operational costs, and economical use of gas in the lift. For example, the energy costs for the inventor""s system pumping a shallow well at a depth of 1400 feet required only one kilowatt-hour of electrical energy to lift a barrel of oil to the surface and at today""s costs, the cost of energy to run a compressor with this system was less than $0.10 per barrel of oil lifted. Obviously, if gas is available for running the compressor, the electrical costs can be reduced or eliminated. Professor Juvkam-Wold of Texas AandM University analyzed the inventor""s data obtained for gas lifting a shallow 860 feet depth well and obtained an amazingly low gas/fluid ratio of only 327 standard cubic feet of gas per barrel of oil produced.
Beam pumps have the major advantage that one usually needs only to turn on the electricity and the system pumps until the liquid is pumped-off from the bore hole. Few beam pumps operate on wells where the liquid level in the bore hole is monitored, and the pumps usually just operate a certain length of time to pump-off the liquid.
Numerous gas lift systems exist and primary inventors and United States patents are: Ridley, U.S. Pat. No. 5,860,795; Jennings, U.S. Pat. No. 5,337,828; Buckman, U.S. Pat. Nos. 4,842,487 and 5,006,046 and Morgan, U.S. Pat. No. 3,941,510. An excellent source concerning the design of gas lift systems and valves is the xe2x80x9cCAMCO GAS LIFT MANUALxe2x80x9d written by Herald W. Winkler and Sidney Smith, CAMCO, INCORPORATED, 7010 Ardmore, Houston, Tex. 77021. Daniel Oil Tools Company located at 153 South Long Drive, Lafayette, LA 70505 is also producer of gas lift valves along with many other oil field tools.
A difficulty with most intermittent gas lift systems is that because of their complexity, it takes more knowledge and skill to design and operate the system. A very major problem for gas lift systems is that they get overloaded with the liquid in the well, that is, too much liquid accumulates into the well and when the system goes to pump the hydrostatic head is too great for the applied pressure. This occurs if there is a rush of liquid into the well for any reason. Also, if the system has been off for any amount of time because of shut-in due to production constraints, because of lack of electrical power due to weather, or for any other numerous reasons, the well often becomes overloaded with liquid and excessive pressure is required to unload the well. A common method used in the field to unload a well is to swab it, which is a tedious and very messy process.
Monitoring the liquid level in a well and pumping at appropriate times reduces the probability of overloading the gas lift pumping system and enables improved production from the well. Buckman uses in U.S. Pat. Nos. 4,842,487 and 5,006,046 an electrical thermistor in the shallow wells with his pumping systems. A problem with this method is maintaining the sensor downhole. Sonic methods have been used for decades to determine the liquid level in wells. U.S. Pat. Nos. 5,121,340; 4,700,569; 4,934,186 and 4,408,676 are representative patents illustrating the methods and technology in measuring liquid levels using acoustic and ultrasonic techniques. In U.S. Pat. No. 4,934,186, McCoy uses a pop gun assembly to initiate a pressure pulse and a microphone at the top of the well to detect the reflected pulses from tubing collars and from the top of the liquid in the well.
What is needed is a gas lift system that automatically and accurately measures the liquid level in the well and maintains the proper level to enhance the production of liquid/gas from that well. The system should also have the ability to unload the liquid from the well regardless of the amount of accumulation in the well. The system must also be energy efficient as well as conserving of gas during pumping.
This invention is an intermittent gas lift system for pumping liquids from shallow wells and it has a gas line, an accumulator, a liquid discharge line and a battery operated controller. The lower part of the gas line has a constriction and a pressure transducer is at the top of the gas line. By measuring reflection time intervals of the reflected pulses from the constriction, the bottom end of the gas tube and, subsequently, reflection from the top of the liquid once it rises inside the gas tube, accurate liquid levels in the gas line and the bore hole can be determined to enable the pumping cycle to be initiated for maximum production. Bypasses are connected between the gas line and the liquid discharge line. Each bypass contains a pressure valve that opens at a set absolute pressure from the pressure in the gas line, an orifice, and a one-way valve to enable the pressure activated valve to operate at appropriate gas line pressures. Bypasses are strategically placed at different elevations to eliminate the potential of overloading the system. Overloading the system occurs when the liquid hydrostatic head due to the liquid slug in the second tube becomes greater than the pressure available to be applied in order to pump the slug from the well. A liquid slug sensor at the top of the discharge line and a rabbit traveling in the liquid discharge line enables optimum production and gas conservation.
The primary object of the present invention is to provide a low cost and energy and gas efficient method for removing liquids from shallow gas or oil wells. The present invention uses a rather unique apparatus and method to accurately determine the height of the liquid in the bore hole and the appropriate time to initiate pumping to enable optimum production. Elements also exist in the present invention to enable the system to continue to pump with optimum efficiency and to overcome the overload condition which handicaps many gas lift systems. Elements also exist in this system to terminate the pumping cycle at the appropriate time so as to increase production and also to conserve gas due to gas blow-by at the end of the pumping cycle.